The present invention relates to a top stabilized photochromic lens system, a method for making the same and a coating material.
Unfortunately, some would think, our enjoyment of the xe2x80x9cGreat Outdoorsxe2x80x9d is often subject to the vagaries Mother Nature throws at us with her different types of weather. Even on a bright sunlit day, for instance, people attempting to enjoy an outdoor activity often have to cope with excessive brightness and glare. To combat this, and increase their outdoor enjoyment, record numbers of people are utilizing sunglasses of one type or another. Many are turning to sunglasses that have a photochromic capability, that is, a capability to darken or lighten based on the level of light intensity. This affords these individual the ability to move from one area of light intensity another area of light intensity without having to continually put-on or take-off their sunglasses. This is especially important for individuals who must wear glasses for corrective reasons.
Currently, however, photochromic lenses are subject to degradation in that the photochromic property of the lens soon wears out. That is, the lenses lose their ability to lighten and darken according to the level of light intensity due to problems of fatigue resistance and oxidation inherently associated with the photochromic compounds utilized. This can lead to a lens which becomes discolored (e.g., spotted), opaque, and/or which even reverses color (e.g., continually dark). It was discovered, however, that through the use of tertiary amine compounds the life of the photochromic compounds could be extended somewhat. U.S. Pat. No. 5,266,447, discloses that photochromic compounds are dissolved or dispersed with a specific tertiary amine compound in a high-molecular compound (i.e., a binder). As disclosed in this patent, the organic photochromic compound is comprised of either a spirooxazine, spiropyran or thiopyran compound, while the tertiary amine compound with which it is mixed may be a hindered amine light stabilizer (HALS) or an ultraviolet (UV) blocker of a variety of types. While effective to a degree, degradation still occurs over time.
Attempts to further stabilize the photochromic compounds beyond the above have failed or so far met with only limited success. For instance, U.S. Pat. No. 5,770,115, relates to a photochromic napthopyran and stabilizer composition. The stabilizer, as disclosed in this patent, is a composition comprised of a polyphenolic antioxidant material, a UV light absorber, and a HALS, each in varying percentages. A sufficient amount of the stabilizer, however, must be used in order to be effective at reducing fatigue resistance of the photochromic material. However, even when the sufficient amount of stabilizer is present with the photochromic material, it is disclosed that only a limited percentage amount of fatigue resistance is achieved.
Another example is U.S. Pat. No. 5,905,148, which relates to polysiloxane copolymers containing both photochromic and light-stabilizing groups incorporated through a hydrocarbon spacer in order to enhance UV light fatigue resistance. The photochromic group is made up of differing spironaphto-oxazines, while the light stabilizing group is made up of HAL""s. As this patent is only recently published it remains to be seen as to the effectiveness of the method disclosed therein to reducing UV light fatigue.
In each of the above mentioned patents, however, the photochromic light stabilizers (i.e., the HALS, which also has an anti-oxidant function and UV absorbers) are always intimately mixed with the photochromic compounds or provided in a layer inside the substrate providing the photochromic compounds. This is insufficient to prevent complete, or even substantial, degradation of the photochromic ability of the compound over time in that the spectrum of light radiation is only partially filtered out (or not at all) and is able to impact the dye molecules solely dependent upon their placement in relation to one another in the compound/layer.
Accordingly, the present invention provides a method and coating solution by which the life of a photochromic compound can be increased dramatically through a top-down stabilization system. The stabilization system is constructed so that the light radiation must first pass through a protective top-coat before reaching any light-sensitive photochromics in the layers below. In this manner then, those light rays deemed harmful to the properties of the photochromic dyes are effectively filtered out, while only the maxima of the light wave (i.e., that needed to activate the photochromic dye) is passed through.
Thus, in construction, a first layer, the base layer is fashioned containing the photochromic dye to be protected by either a coating of a lens with the dye or an imbuing of the dye into the lens material itself. This layer can also contain anti-oxidants, HALS and/or UV absorbers. On top of this, a second layer, the top layer, is fashioned containing a hindered amine light stabilizer (HALS) and/or a ultraviolet (UV) light absorber. Accordingly, light radiation must first pass through the protective coating containing the HALS and/or UV absorber.
The present invention, including its features and advantages, will become more apparent from the following detailed description with reference to the accompanying drawings.